This work investigates tibiofemoral joint kinematic deviations across two walking conditions, Normal, and Fast, using the Gait Deviation Index (GDI). The primary objective was to assess the sensitivity of the GDI to variations in speed with a focus on intra-subject comparisons. Motion capture data from one healthy adult was recorded using a Vicon system and analyzed using a Joint Coordinate System (JCS) framework. Gait cycles for both conditions were segmented based on heel strike events and time-normalized to enable consistent comparison. The knee flexion angle for each cycle was computed. Singular Value Decomposition (SVD) was applied exclusively to control data from the normal condition to extract dominant mode shapes. Gait Deviation Index scores were then computed for each stride during the Fast walking condition relative to the Normal walking. The resulting average GDI score for the fast condition was approximately 88.89, which falls close to one standard deviation of the reference value of 100. This suggests that although the amplitude of joint angles differed, the underlying movement patterns remained largely consistent across conditions. These findings highlight the GDI score as a sensitive and interpretable method for detecting kinematic inconsistency induced by walking speed.